For many years conventional magnetic storage devices have been used to store data and information. Magnetic storage devices generally include a magnetic medium with units (e.g., bits) of magnetic material that can be polarized to distinct magnetic states. The direction of the magnetization points in different directions, which can be referred to as a positive state and a negative state, respectively. Each bit can store information (generally binary information in the form of either a 1 or a 0) according to the magnetic polarization state of the bit. Accordingly, magnetic storage devices generally include a “read” element that passes over the magnetic material and perceives the magnetic polarization state of each bit and a “write” element that passes over the magnetic material and changes the magnetic polarization state of each bit, thereby recording individual units of information. Therefore, the amount of information that can be stored on a magnetic storage medium is proportional to the number of magnetic bits on the magnetic storage medium.
There are various types of magnetic storage media and each type involves different fabrication techniques. For example, conventional granular magnetic recording media are disks that have multiple grains in each magnetic bit. In granular magnetic media, all of the domains are co-planar and the surface of the disk is relatively continuous. In order to increase the amount of information that can be stored on a granular magnetic disk, the number of grains per magnetic bit can be decreased while keeping the grain size approximately the same. However, with fewer grains in each bit, there is decreased signal-to-noise ratio (e.g., less signal and more noise). In order to maintain a better signal to noise ratio, methods have been developed that decrease both the size of the magnetic bit and the size of the individual grains making up each magnetic bit, thus keeping the same number of grains in each magnetic bit. However, when the grains become too small, thermal fluctuations can cause the grains to spontaneously reverse polarity, thus resulting in unstable storage and a loss of information.
Bit-patterned media (BPM) is another example of magnetic storage media. In bit-patterned media, each bit is a single magnetic domain rather than a collection of contiguous magnetic grains. The BPM bits can be topographically patterned using lithographic and etching techniques to form magnetically isolated bit islands surrounded by trenches. In some instances, the trenches are formed by etching away a magnetic material. In yet other instances, the physical patterns are etched into a non-magnetic substrate and then a magnetic material is coated over the patterned substrate. Because of the physical separation between the elevated bit islands and the trenches, the width of each distinct bit island can be decreased in order to increase the areal bit density of the device, while still maintaining a high signal-to-noise ratio and high thermal stability.
Another type of BPM is ion-implanted BPM. With ion-implanted BPM, instead of actually etching the surface of the magnetic layer to form trenches and elevated islands, the trench regions are instead exposed to ion-bombardment, which changes the morphology of the magnetic layer without etching it away. In other words, the ions impacting the trench regions damage the crystalline structure, the chemical order, and/or the chemical, electronic, or band-structure properties of the magnetic layer in order to at least reduce the ferromagnetic properties in the trench regions, thus yielding a similar magnetic contrast between the island regions and the trench regions that exists in etched BPM.
Although ion-implantation processes provide distinct benefits, such processes can degrade the magnetic properties in the island regions as the impacting ions damage the side walls of the island regions. For example, the concentration of implanted ions is distributed and changes across a small yet finite spatial dimension in the region near the edge of the implantation (i.e., the boundary regions between the island regions and the trench regions). This is referred to as straggle. The amount of damage or change to the chemical order and the composition itself varies across this spatial dimension. In other words, conventional ion-implantation processes generate magnetic media that, because of the concentration gradient of the implanted ions and the degraded magnetic properties at the peripheral boundaries of the island regions, are susceptible to spontaneous magnetic polarity reversal, thermal instabilities, and/or reduced magnetic volume.